Installing a reference sensor

To further develop the readout circuitry and options for the data logger and the sensors, we installed one reference site in Linköping such that we can do local trials. The whole was dug in a lawn, some 50m away from the closest fields. These fields are currently mainly used to grow silage.

We did not dig the hole too deep in this case, we just want to study how the sensors can be calibrated and mainly to interact with the logger through our mobile phones. We will also have reference values available to align with the sensors in South Africa. We dig down three different sensors, EC-5, 10HS, and 5TE from Decagon. The reference values with open-air humidity and fully submerged in water are given in the table. The different sensors give slightly different results but they are also designed for different volumes. Saturated values are fairly identical.

Sensor type	Depth	Open-air [cub-m/cub-m]	Submerged [cub-m/cub-m]	Temp [C]
EC-5	10cm	-0.140	0.574	N/A
10HS	40cm	-0.279	0.505	N/A
5TE-h	60cm	-0.023	0.518	28.7

Some 30 minutes after installation, we could measure these values from the sensors.

Sensor type	Depth	Dug down [cub-m/cub-m]	Temp [C]
EC-5	10cm	0.217	N/A
10HS	40cm	0.210	N/A
5TE-h	60cm	0.020	19.3

Luckily, we got help from a field application engineer to install the sensor and mainly dig. It was also useful to have help when sorting out which cable goes to which sensor. Sort of.

Below we find the final view of the installed sensor station (bar the straps being shortened). There is an ECRN-50 rain gauge from Decagon on the top. It was slightly damaged in a car incident and we have to check if it works properly, otherwise we need to ship it for service.

We need to also verify the ECRN-50 rain gauge.